Television, computer games and the internet are common components of the home environments of most children. Sedentary behaviors such as watching television and movies and playing video games are associated with the increased prevalence of pediatric obesity. Controlled laboratory and clinical research has shown that reducing these sedentary behaviors is associated with reductions in percent overweight in those who are obese and decrease in rate of BMI increase in non-obese children. There has been no research designed to test the influence of reducing television watching and other sedentary behaviors on prevention of obesity or further weight gain in overweight or obese youth. The aim of this study is to test an innovative environmental intervention designed to modify the home television watching and computer game use environment in contrast to a control condition. Seventy-two overweight or obese 4-7 year-old boys and girls will be randomized to an environmental intervention that focuses on reduction of television and home movie watching and computer games versus a control intervention. The environmental intervention is designed to gradually reduce targeted sedentary behaviors to 50% of baseline levels. We hypothesize that reducing sedentary behaviors will result in a stabilization or smaller increase in BMI in comparison to an untreated control group followed over two years. In addition, we predict lower energy intake for those in the intervention versus control groups, and an increase in physical activity when sedentary behaviors are decreased for the intervention group, and a further decrease in physical activity as the children in the control group become older. We also predict that children who often eat in association with targeted sedentary behaviors will show the largest decreases in energy consumed when sedentary behavior is decreased, and that children with a high baserate of targeted sedentary behaviors and low baserate of physical activity will be more likely to increase physical activity when sedentary behaviors are reduced.